The invention concerns a new liquid composition containing diisocyanates having a diphenylmethane structure obtained by the initial reaction of a benzyl halide with benzene, followed by a nitration of the aromatic rings, a hydrogenation and a phosgenation. The composition can be used to produce polyurethanes.
Some diisocyanates of diphenylmethane aromatic hydrocarbon structure (M.D.I.) are already being synthesized industrially and they are obtained by the condensation of two molecules of aniline with one of formaldehyde in the presence of an acid catalyst, followed by a phosgenation, leading to mixtures containing 4,4',2,4', and 2,2' isomers. But this condensation is never totally selective in 2-ring products and a mixture of polyisocyanates and diisocyanates is usually synthesized with the latter being separated by distillation in order to yield pure M.D.I. The 4,4' M.D.I. isomer generally is present in the largest amount and possesses a melting point of 38.degree. C. Thus, depending on its concentration, it may be necessary to liquefy the mixture of diisocyanates before being able to use it, either by melting it or by transforming it chemically. Moreover, such solid mixtures do not stand storage very well and must be preserved in a cold chamber.